Optical information processing apparatus in which the output of an optical sensor is replaced by a reference signal during the occurrence of malfunction

ABSTRACT

An optical information processing apparatus effects recording and/or reproduction of information by scanning information tracks of an optical recording medium by at least one condensed light beam while effecting tracking and/or focusing control. The apparatus comprises at least two groups of optical sensors for receiving the light of the light beam reflected. By the medium, a circuit for producing a signal for effecting the control from the output of each of the groups of optical sensors, a reference signal generating source, and a switching circuit for causing, when at least one of the outputs of the groups of optical sensors exhibits an abnormal value, the reference signal, instead of the at least one output, to be input to the control signal producing circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical information processing apparatusfor effecting recording and or reproduction of information by scanningthe information tracks of an optical recording medium by at least onecondensed light beam while effecting tracking and/or focusing control.

2. Related Background Art

In recent years, commercialization and development of opticalinformation processing apparatuses such as electronic file systemsutilizing compact discs or postscript type discs and optical discsystems using erasable magneto-optical materials or phase shift typematerials have been flourishing.

Also, attention has recently been paid particularly to an optical cardsystem which effects the recording and reproduction of information on anoptical recording medium in the form of a card (hereinafter referred toas an optical card). The optical card is characterized by its ease ofportability resulting from its form, and its greater information storagecapacity per area than a disc.

Recording is effected on the above-described recording medium by suchthat a light beam modulating in accordance with recording information.The light beam is converged into a minute spot and is scanned on thesurface of the medium, whereby information is recorded as opticallydetectable record pit rows (information tracks). In such case, in orderto record the information accurately without any problems such asintersection between the information tracks, it is necessary to controlthe applied position of the light beam in a direction perpendicular tothe scanning direction (tracking control). It is also necessary tocontrol the applied position of the light beam in a directionperpendicular to the surface of the optical card (focusing control) inorder to apply the light spot as a minute spot of stable size in spiteof any bending or mechanical error of the optical card. Tracking andfocusing controls are also necessary during reproduction.

FIG. 1 of the accompanying drawings is a schematic view showing anexample of the construction of an optical information processingapparatus provided with tracking and focusing control means. Such anapparatus is described in detail, for example, in Japanese Laid-OpenPatent Application No. 62-239333 (corresponding U.S. Application Ser.No. 33,789, which was abandoned in favor of U.S. Application Ser. No.479,205).

In FIG. 1, a light beam emitted from a light source 1 such as asemiconductor laser is collimated by a collimator lens 2 and dividedinto three beams by a diffraction grating 3. These divided light beamsare reflected by a beam splitter 4, are condensed on an optical card 6by an objective lens 5 and forms three beam spots S₁, S₂ and S₃. Thelight beams reflected by the optical card 6 again pass through theobjective lens 5 and are transmitted through the beam splitter 4,whereby they are separated from the incident beams. These reflectedbeams are reflected by a mirror 7, are condensed by a sensor lens 8 anda cylindrical lens 9 and enter optical sensors 10₁, 10₂ and 10₃. Theseoptical sensors 10₁, 10₂ and 10₃ are disposed so as to receive the lightbeams from the beam spots S₁, S₂ and S₃, respectively.

The light receiving surface of the optical sensor 10₂ is divided intofour sections as shown in FIG. 2 of the accompanying drawings, and thesum of the detection signals of the two sets of opposed light receivingsurfaces is differentiated, whereby astigmatism introduced by theaforementioned cylindrical lens 9 is detected and a focusing signal isobtained by the principle of the known astigmatism method described inU.S. Pat. No. 4,023,033, for example, also, when the information is tobe reproduced, a reproduction signal is obtained from the optical sensor10₂. The detection signals of the optical sensors 10₁ and 10₃ aredifferentiated by a differential amplifier 11, and output as a trackingsignal S_(T) from a terminal 12. This tracking signal S_(T) and theaforementioned focusing signal are fed back to a lens actuator 18 by acircuit, not shown, and the objective lens 5 is moved in a directionperpendicular to the optic axis and in the direction of the optic axis,whereby tracking and focusing controls are accomplished.

The optical card 6 is reciprocally moved in the direction of arrow R bya driving mechanism, not shown, whereby the light spots S₁, S₂ and S₃scan on the optical card. Also, an optical head 19, including theaforedescribed optical system, is designed so as to be movable in adirection perpendicular to the direction of arrow R, i.e., a directionperpendicular to the plane of the drawing sheet in FIG. 1, for thepurpose of track access.

FIG. 3 of the accompanying drawings is a plan view of the optical card6. The optical card 6 comprises a substrate formed of plastics or thelike, and a recording layer 20 of silver salt, dyestuff or the likeformed on the substrate. On the recording layer 20, there are preformeda plurality of parallel tracking tracks 21 optically detectable by theirunevenness or the difference in reflectance with respect to the adjacentportions of the card. These tracking tracks 21 are disposed at equalintervals, and a recording area in which information may be recorded isprovided between the adjacent tracking tracks.

FIG. 4 of the accompanying drawings is an enlarged view of the recordingsurface of the optical card 6 illustrating the recording process usingthe apparatus of FIG. 1. There are recording areas 22₁ and 22₂ betweenthe tracking tracks 21₁, 21₂ and 21₃ The beam spots S₁ and S₃ areapplied so as to partly overlap the tracking tracks 21₁ and 21₂, and thebeam spot S₂ is applied to the recording area 22₁. If the appliedpositions of the beam spots S₁ -S₃ deviate in a direction perpendicularto the tracks, there occurs an imbalance between the quantity of lightof the reflected beam from the spot S₁ and the quantity of light of thereflected beam from the spot S₃. Accordingly, by differentiating asignal obtained by detecting the lights from these spots as shown inFIG. 1, there is obtained a tracking signal S_(T) indicative of theamount and direction of the deviation. By moving the objective lens onthe basis of this tracking signal, the beam spot S₂ is accuratelydirected to the recording area between the tracking tracks andinformation can be recorded as indicated by record pits 23. Wheninformation is to be recorded in the recording area 22₂, the beam spotsS₁, S₂ and S₃ may be applied to the tracking track 21₂, the recordingarea 22₂ tracking track 21₃, respectively. The light intensitydistributions of the beam spots S₁ and S₃ on the optical card areusually Gaussian distributions which are high in the central portion andtherefore, if these beam spots are rendered so that one half of each ofthe beam spots overlaps the tracking track, the variation in quantity oflight by track deviation is great and tracking signal detection of highsensitivity can be accomplished.

Now, in the method of detecting the tracking signal as described above,when there is a defect in the tracking tracks, there has been theundesirable possibility that the beam spot S₂ for recording andreproduction deviates from the recording area 22₁.

Such a situation is shown in FIG. 5 of the accompanying drawings. FIG. 5shows a situation in which a defective portion 25 is in the trackingtrack 21₁ shown in FIG. 4 and FIG. 5 further shows times t₀ -t₁corresponding to the scanning position of the beam spot S₁ applied tothis track.

The reflectance of the defective portion 25 is lower than that of thenormal or unaffected portions of tracking tracks 21₁ and 21₂.

At the time t₀, the spot S₁ overlaps a normal or unaffected portion ofthe track 21₁. Next, when at the time t₁, the spot S overlaps thedefective portion 25, there arises an imbalance between the quantity oflight of the reflected beam from the spot S₁ and the quantity of lightof the reflected beam from the spot S₃, whereby a fluctuation occurs inthe applied position of the spots to effect an auto tracking operation.However, if as shown, the defective portion 25 is relatively wide, attime t₁ ', the spot S₂ will deviate from the recording area 22₁ andnormal recording and reproduction of information will become impossible.

Also, the situation in which an abnormality occurs in the controloperation due to such defect or the like of the medium as describedabove might also affect the focusing control.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above-notedproblems peculiar to the prior art and to provide an optical informationprocessing apparatus which can effect tracking and/or focusing controlnormally even when there is a defect in a medium.

The above object of the present invention is achieved by an opticalinformation processing apparatus for effecting the recording and/orreproduction of information by scanning the information tracks of anoptical recording medium by at least one condensed light beam whileeffecting tracking and/or focusing control. The apparatus comprises atleast two groups of optical sensors for receiving the light of the lightbeam reflected by the medium, a circuit for producing a signal foreffecting control from the output of each of the groups of opticalsensors, a reference signal generating source, and a switching circuitfor causing, when at least one of the outputs of the groups of opticalsensors exhibits an abnormal value, the reference signal, instead of theat least one output, to be input to the control signal producingcircuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of the construction of anoptical information processing apparatus according to the prior art.

FIG. 2 is a schematic view showing the construction of optical sensorsin the apparatus shown in FIG. 1.

FIG. 3 is a plan view of an optical card used in the apparatus shown inFIG. 1.

FIGS. 4 and 5 are schematic views illustrating the manner of trackingcontrol in the apparatus shown in FIG. 1.

FIG. 6 is a schematic diagram showing an embodiment of a trackingcontrol circuit used in the apparatus of the present invention.

FIGS. 7A-7C show the states of beam spots when a defective track isscanned in the present invention and signal wave forms in variousportions of the then circuit of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 6 is a schematic diagram showing an embodiment of a trackingcontrol circuit used in the apparatus of the present invention. Theapparatus of the present invention can be made similar in constructionto the prior-art apparatus, except for this circuit. FIG. 7A shows thestates of beam spots when a defective track is scanned, and FIGS. 7B and7C show the corresponding signal wave forms of various portions of thecircuit of FIG. 6. In FIGS. 6 to 7C, members identical to those in FIGS.1 to 5 are given identical reference characters and need not bedescribed in detail.

In FIG. 6, the reflected beams from beam spots S₁ and S₃ applied totracking tracks 21₁ and 21₂, respectively, shown in FIG. 7A are receivedby optical sensors 10₁ and 10₃ and output as signals A₁ and A₃,respectively. The optical sensors 10₁ and 10₃ are connected to adifferential amplifier 11 through switches 27₁ and 27₃ and also areconnected to malfunction detectors 26₁ and 26₃, respectively. The outputterminals of the malfunction detectors 26₁ and 26₃ are connected to theswitches 27₁ and 27₃, respectively.

The malfunction detectors 26₁ and 26₃ are designed to output detectionsignals C₁ and C₃, respectively, when the voltages of the signals A₁ andA₃ from the optical sensors 10₁ and 10₃ greatly deviate from apredetermined value.

Voltage sources 24₁ and 24₃ are connected to terminals of the switches27₁ and 27₃, respectively, and voltages V₁ and V₃ equal to the voltagesof the signals A₁ and A₃ when the signals detected by the opticalsensors 10₁ and 10₃ are normal are output from the respective voltagesources. The switches 27₁ and 27₃ are designed to be connected to thevoltage sources 24₁ and 24₃ when the detection signals C₁ and C₃ fromthe malfunction detectors 26₁ and 26₃ are output so that the voltages V₁and V₃ are supplied to the differential amplifier 11.

In such a construction, the switches 27₁ and 27₃ are connected so as tosupply the signals A₁ and A₃ output from the optical sensors 10₁ and 10₃when these signals A₁ and A₃ exhibit normal values, and are connected soas to supply the voltages V₁ and V₃ output from the voltage sources whenthe voltages of the signals A₁ and A₃ from the optical sensors 10₁ and10₃ deviate greatly from a predetermined value.

Accordingly, for example, when the signal A₁ detected from the opticalsensor 10₁ exhibits an abnormal value due to a defect of the trackingtrack 21₁ when tracking is effected, the voltage V1₁ of a predeterminedvalue produced from the voltage source 24₁ can be used instead of thesignal A1₁ which has exhibited the abnormal value to produce a normalservo error signal.

The operation of the tracking circuit will now be described withreference to FIGS. 7A to 7C.

In FIG. 7A, the reference numerals 21₁ and 21₂ designate the trackingtracks, the reference numeral 22₁ denotes a recording area, and S₁, S₂and S₃ show the locations at which beam spots are applied to thesetracks and the recording area at times t₀, t₁, t₂ and t₃. In FIG. 7A, adefective portion 25 is created at a location on the tracking track 21₁which corresponds to the times t₁ -t₂. It is to be understood that inthe tracking track 2₁, the other portion than the defective portion 25is a normal portion.

FIGS. 7B and 7C show the voltage of the signal A₁ and the voltage of thesignal B₁ which correspond to the above-described change in time.

At the time t₀, the spot S₁ partly overlaps the normal portion of thetrack 21₁. In this case, the detection signal C₁ is not output from themalfunction detector 26, and the switch 27₁ inputs the detection signalA from the optical sensor 10₁ as the signal B₁ to the differentialamplifier 11.

Next, at the time t_(l), when the spot S₁ partly overlaps the defectiveportion 25, the voltage of the signal A₁ decreases and the malfunctiondetector 26₁ operates and outputs the detection signal C₁. Thereby, theswitch 27₁ is changed over to the voltage source 24₁ side and thevoltage V₁ is input to the differential amplifier 11. Since this voltageV₁ exhibits the same value as a signal A₁ when the detection signal fromthe optical sensor 10₁ exhibits a normal value, no change occurs to thesignal B_(l) output from the switch 27₁ and therefore, the spot S₂ doesnot deviate from the recording area.

In this case, the voltage V₁ exhibits a predetermined value, but in theoptical sensor 10₃, the signal A₃ from this optical sensor 10₃ is inputas signal B₃ ; to the differential amplifier 11 and therefore, thisstate can be said to be a state in which the tracking servo isoperating. However, in this state, the tracking servo gain is 1/2 andtherefore, the amplification degree of a circuit, not shown, can bedoubled to thereby keep the tracking servo gain constant.

When at the time t₂, the spot S₁ leaves the defective portion 25 and thevoltage of the signal A₁ increases, the signal C₁ is not output from themalfunction detector 26₁ and the switch 27₁ changes over to its originalstate and inputs the signal A₁ from the optical sensor 10₁ to thedifferential amplifier 11.

At the time t₃, the circuit is in the same state as that at the time t₀.

The tracking control portion used in the foregoing description has beendescribed with respect to the tracking signal detection when there is adefect in one tracking track 21₁. but when there is a defective portionin the other tracking track 21₂ , the malfunction detector 26₃, thevoltage source 24₃ and the switch 27₃ operate in the same manner asdescribed above.

While the tracking control circuit has been described above, the presentinvention is also applicable to a focusing control circuit. In suchcase, for example, in the optical sensor 10₂ shown in FIG. 2, the sumsignals of the two sets of opposed light receiving surfaces are used asthe signals A₁ and A₃. respectively, of the circuit shown in FIG. 6. Afocusing signal is output from the differential amplifier 11 toward alens actuator.

The present invention permits various applications besides theabove-described embodiment. For example, the tracking signal and thefocusing signal may be detected not only by the aforedescribedthree-beam method and astigmatism method, but also by other methods.

The present invention covers all such applications without departingfrom the scope thereof as defined in the appended claims.

What is claimed is:
 1. An optical information processing apparatus foreffecting the recording and/or reproduction of information by scanninginformation tracks of an optical recording medium by at least onecondensed light beam while effecting tracking and/or focusing control,said apparatus comprising:at least two groups of optical sensors forreceiving light of the light beam reflected by the medium and forgenerating respective output signals; a control signal producing circuitfor producing a signal for effecting the tracking and/or focusingcontrol using the output signal of each of said groups of opticalsensors; a plurality of reference signal generating sources forgenerating a plurality of reference signals; and a switching circuit forcuasing, when at least one of the output signals of said groups ofoptical sensors exhibits an abnormal value, a respective referencesignal, instead of the at lest one output signal having an abnormalvalue, to be input to said control signal producing circuit.
 2. Anoptical information processing apparatus according to claim 1, whereinsaid switching circuit selects at least one of the output signals ofsaid groups of optical sensors and the reference signal to be input tosaid control signal producing circuit, and further comprising a switchand a malfunction detector for controlling change-over of said switch.3. An optical information processing apparatus according to claim 2,wherein said malfunction detector outputs a detection signal to saidswitch if at least one of the output signals of said groups of opticalsensors deviates greatly from a predetermined value.
 4. An opticalinformation processing apparatus according to claim 1, wherein themagnitude of the reference signal is set so as to be equal to themagnitude of the output signals of said groups of optical sensors whensaid optical sensors are operating normally.
 5. An optical informationprocessing apparatus according to claim 1, wherein the servo gain of thetracking and/or focusing control is doubled when the reference signal isinput to said control signal producing circuit.
 6. An opticalinformation processing apparatus according to claim 1, wherein threelight beams are applied to the medium, and said groups of opticalsensors include two optical sensors for receiving reflected light of twoof the three light beams.
 7. An optical information processing apparatusfor effecting the recording and/or reproduction of information whileconverging a light beam emitted from a light source onto a recordingmedium by an objective lens and effecting tracking and/or focusing servocontrol of the light beam, said apparatus comprising:an optical sensorfor receiving light of the light beam reflected by the medium and forgenerating an output signal; a tracking and/or focusing error signalgenerating circuit for generating a tracking error signal and/or afocusing error signal from the output signal of said optical sensor; alens actuator for moving the objective lens in a tracking and/orfocusing direction on the basis of the generated tracking error signaland/or focusing error signal, wherein said optical sensor, said lensactuator and said tracking and/or focusing error signal generatingcircuit comprise a tracking and/or focusing servo control loop; anabnormality detecting circuit for detecting an abnormality of a signalcorresponding to the output signal of said optical sensor; a switchingcircuit for opening said tracking and/or focusing servo control loopwhen said abnormality detecting circuit detects an abnormality of thesignal corresponding to the output signal of said optical sensor; andreference signal generating means for supplying a predeterminedreference signal to said lens actuator when said tracking and/orfocusing servo control loop is opened by said switching circuit.
 8. Anoptical information processing method for effecting the recording and/orreproduction of information while converging a light beam emitted from alight source onto a recording medium by an objective lens and effectingtracking and/or focusing servo control of the light beam, said methodcomprising the steps of:receiving light reflected from the recordingmedium by a plurality of sensors and generating respective outputsignals; generating a tracking error signal and/or a focusing errorsignal from the respective output signals of the plurality of sensors;detecting any abnormality of the respective output signals of theplurality of sensors; and generating a tracking error signal and/or afocusing error signal by using a predetermined reference signal, insteadof the respective output signal of each sensor whose output signalexhibits an abnormal value, when detecting an abnormality of therespective output signal of at least one of the plurality of sensors.